AEMCA Practice Exam

What is the mechanism of action of diphenhydramine?

1. Blocks alpha receptors

2. Inhibits Histamine H1 receptors

3. Stimulates beta receptors

4. Acts directly on pain receptors

The correct answer is: Inhibits Histamine H1 receptors

Diphenhydramine functions primarily as an antihistamine by inhibiting Histamine H1 receptors. Histamine is a chemical that plays a key role in allergic reactions and can cause symptoms such as itching, sneezing, and increased mucus production. By blocking these receptors, diphenhydramine effectively reduces the effects of histamine, alleviating allergic symptoms. Additionally, because it crosses the blood-brain barrier, diphenhydramine can also have sedative effects, which is why it is often used in treating insomnia or as a pre-medication for its calming properties. This mechanism of action highlights its effectiveness in providing relief from allergies while also inducing drowsiness, making it useful in various clinical settings.